Medical guide element with diameter transition

ABSTRACT

Improved medical filaments for use with dilators to be inserted into a patient, for example into the vascular lumen, are provided, as well as combinations of filaments and dilators. Methods for use of such filaments and filament-dilator combinations are also described. The filament includes a proximal segment and a distal segment. The diameter of the distal segment is greater than the diameter of the proximal segment. The change in diameter is abrupt, providing a discrete step transition at a point along the filament which presents a proximally-facing surface on the distal segment. When the proximal segment of the filament is fully inserted into a dilator having a distal tip adapted for insertion into a patient, the dilator distal tip firmly abuts the proximally-facing end surface of the distal segment. The relative dimensions of the dilator tip and the discrete stepped transition of the filament provides full shielding or over shielding of the dilator tip, thereby facilitating passage of the dilator tip along the tissue track, through the puncture hole and into the orifice.

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 12/233,272 filed Sep. 18, 2008, which ishereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to apparatus and methods for insertingcatheters into the human body employing percutaneous techniques forvascular access. More particularly, the invention relates to a novelintroducing guide element and to novel combinations of said introducingguide element with a matching dilating catheter.

BACKGROUND

In present medical practice, insertion of catheters into blood vesselsand other body structures is most often accomplished by the percutaneoustechnique. The Percutaneous Technique is a term of art for atranscutaneous method that avoids surgical cut-down and dissection.Instead, a hollow-bore needle is employed to penetrate the skin orsurface, traverse the subcutaneous tissue and other interveningstructures, and enter the lumen of the blood vessel or body structure.Then a tracer or flexible filament, typically in the form of a metallicguidewire, is inserted through the bore of the needle so that it entersthe vascular lumen and extends into the lumen to a distance sufficientto prevent accidental or inadvertent dislodgement. The flexibility ofthe guidewire reduces the likelihood of injury to the interior surfaceof the blood vessel within which it is advanced and manipulated toensure a secure position. After the guidewire has been inserted into thevascular lumen, the practitioner, holding the proximal segment of theguidewire, i.e. the segment residing outside of the human body and abovethe skin, carefully withdraws the needle. Once the needle is entirelyoutside the body, it is slidably withdrawn from the guidewire and setaside. The guidewire now constitutes a smooth rail for slideableinsertion of other devices, such as catheters of various types. Thisconcept and method was innovated by Ivan Seldinger in 1953 and is oftenreferred to as the “Seldinger technique”.

Building upon the original Seldinger technique for percutaneous access,Drs. Donald Desilets and Richard Hoffman in 1965 innovated thecombination of a dilating catheter and a separate, thin-walled tubularconduit, a sheath, carried thereon to gain access to the vascular lumenvia the guidewire. As detailed below, a dilating catheter with aconically tapered tip is advanced over and along the guidewire anddilates the arteriotomy puncture created by the needle up to theselected diameter of the chosen catheter. The main body of the dilatingcatheter carries a thin-walled sheath into the blood vessel. Furtheradvancement of this catheter-sheath combination introduces the sheathinto the blood vessel to a secure indwelling position, whereupon theguidewire and the dilating catheter are removed, leaving the sheath inplace to provide a clear cylindrical path from skin into the vascularlumen. In this manner, the sheath provides a smooth unobstructedpassageway for the insertion of diagnostic and/or therapeutic cathetersand devices into the vascular system.

This procedure is referred to as the “Desilets-Hoffman technique” and isalso referred to as the “modified Seldinger technique” or“Seldinger-Desilets-Hoffman technique”, or simply “SDH technique” aswill be referred to herein. This technique can be applied to accessblood vessels as well as other anatomic structures.

DEFINITIONS

As used herein, the term “percutaneous technique” refers to atranscutaneous method that generally avoids surgical cut-down anddissection.

The term “guide element”, “guiding filament”, or simply “filament”refers to an elongate, flexible member, often metal, such as anintroducing guidewire, as is well known in the art.

The term “distal” refers to a relative position or direction away fromthe practitioner and closer to or towards the patient. When used inreference to a guidewire, the distal end refers to the end of theguidewire inserted into the patient.

The term “proximal” is used to refer to a relative position or directionclose to or towards the practitioner and away from the patient. Whenused in reference to a guidewire, the proximal end refers to the endclosest to and held by the operator.

The terms “dilating catheter” and “dilator” refer to a catheter for usein the SDH technique, which enlarges the tissue track and target orificeto a desired size.

The “target orifice” or “target opening” or “opening” is the hole in theblood vessel or the hole in another anatomic structure that is to bedilated by the dilator. When in the artery it is termed an arteriotomy.

The term “match” or “matching” as used to describe the needle, theguidewire and the dilator of the prior art means that the guidewire isof a diameter, as known in the art, close to but smaller than the boreof the hollow needle so that it can pass through the bore of the hollowneedle and yet substantially block the backflow of blood from theopening and through the needle; and that the hollow bore of the dilatoris of a diameter, as is known in the art, close to but larger than thediameter of the guidewire so that it can pass smoothly over theguidewire.

The Desilets-Hoffman Technique and the Present Art

Vascular access procedures, as currently practiced according to the SDHtechnique, employ four elements or devices: (1) a hollow-bore needle topuncture the blood vessel; (2) a short guidewire which may be referredto as an introducing guidewire; (3) a dilator with a cylindrical mainbody, a hollow bore, a conically-tapered distal portion, and a distaltip having an inner diameter matched to the outer diameter of theguidewire; and (4) a cylindrical, thin-walled, tubular sheath which sitssnugly on the main body of the dilator such that upon dilation of thearteriotomy by the dilator and entry therein, the main body of thedilator supports and carries the thin-walled sheath into the bloodvessel.

As described above, the needle is used to puncture the wall of the bloodvessel or body structure; when in the artery this creates thearteriotomy. Due to the difference between the outer diameter of theneedle and the outer diameter of the guidewire, there can be a gapbetween the perimeter of the puncture created by the needle's outer edgeand the guidewire extending through the puncture. This gap is minimizedby an optimum match of the guidewire to the needle's internal diameter.An elastic vessel may elastically contract around the guidewire toreduce or eliminate the gap, while a less elastic vessel may retain itsoriginal dimension leaving a larger gap. If any gap exists, blood mayflow out of the vessel. This backflow of blood can cause bleeding, ahematoma, pseudo-aneurysm, or other complications. The larger the gapthe more backflow will occur

Contemporary practice of the SDH method for percutaneous entry employs ashort introducing guidewire that is cylindrical and of uniform diameteralong its entire length. The usual prior-art guidewire consists of twoprincipal parts: a cylindrical, longitudinal inner “core-wire” aroundwhich a second wire, called a “coil-wire”, is helically or spirallywound with a tight pitch so that successive turns abut each other,leaving little or no space between each turn so as to create a surfacethat is as smooth and regular as possible. To prevent this helical coilfrom unraveling it is usually bonded by solder or other means to thecore-wire at several points along its length, and most importantly, atthe very distal tip of the assembly. Often, the core-wire has a taperedend toward its distal tip, the taper providing increased flexibility ofthe core wire over the distal few centimeters of length, and thereforeincreased flexibility of the distal end portion of the wire assembly.The constant outer diameter along the entire length of the guidewireensures a good, unvarying fit with the internal diameter of the tip ofthe dilator as it is advanced over the guidewire. Additionally, theguidewire may have a curved distal end portion, referred to as a J-tip,whose length may vary from 2 cm to 5 cm or greater depending on theconstruction of the specific wire. The J-tip maintains the guidewirewithin the main lumen of the major vessel and prevents its distal tipfrom being diverted into a side-branch. Also, the J-tip reduces thepossibility of trauma or vessel perforation because it has a curled endinstead of a discrete tip.

A conventional dilator has a hollow, cylindrical body, often with a hubat its proximal end, and a tapered portion at its distal end, whichtapers from the cylindrical body down to the distal tip, i.e. the outerdiameter at the cylindrical portion is larger than the outer diameter atthe tip. FIG. 1A shows a prior-art assembly of a guidewire 110 insertedthrough a typical dilator 120 having a distal end 130 comprised of adistal tapered portion 132, a distal tip 134 having an outer diameterOD2 and a distal tip opening having an inner diameter ID1. The dilator120 has a cylindrical body 140 and an inner passageway 142. The outerdiameter along the cylindrical body portion of the dilator 120 isrepresented by OD3 which is greater than OD2, the tapered portion 132accounting for this diameter change.

Guidewire 110, comprising core wire 111 and coil wire 112, has an outerdiameter OD1 and is dimensioned such that OD1 is matched to, butslightly less than, the inner diameter of the bore of the needle. Theinner diameter ID1 of the opening at the distal tip 134 is matched tothe guidewire's outer diameter OD1, taking account of the need for someclearance to eliminate sliding frictional forces and allowance for themanufacturing tolerances or other variations from the nominal diametersof each component. It should also be noted that for manufacturingreasons, the extrusion creating the body of the dilator may sometimes befabricated with a bore larger than that required to appropriately matchthe guidewire, in which case the dilator undergoes a secondary operationwhich reduces the diameter of the opening at its most distal portion tomatch the outer diameter of the guidewire with which it will mate.

The cylindrical body of the dilator has an outer diameter, measured inFrench units (3-French units=1.0 mm), corresponding to the diagnostic ortherapeutic catheter to be used later in the procedure. The distal-tipregion of all dilators, regardless of the diameter of the main body,tapers down toward its tip and approaches the outer diameter of theguidewire as closely as possible. However, the dilator's leading tipmust have sufficient wall thickness to maintain its structural integrityas it passes through tissue. Being fabricated of a flexible plastic suchas polyethylene, polypropylene, polyurethane, or the like, the tipcannot be formed with too thin a wall at the very distal tip, as anunduly thin wall will become frayed or deformed as it forciblyprogresses through the skin, subcutaneous tissue, and vascular wall. Forexample, a muscular artery, such as the femoral artery, strongly resistspassage of the distal tip of the dilator. Hence, there must be apronounced difference between the inner and outer diameters of the tipof the dilator thereby creating a wall thickness at the tip ofsufficient substance to maintain the integrity of the tip while itwithstands the forces it encounters during passage, and to prevent itfrom fraying or deforming. As a result, the tip of the dilator mustpresent a relatively annular, forward-facing tip, causing a step-up ordiscrete increase in diameter at the transition to the dilator tip.During insertion into a blood vessel this diameter transition creates adiscontinuity. It engages the outer wall of the blood vessel and mustenter through the smaller hole created by the puncturing needle, throughwhich the guidewire now resides. FIG. 1A illustrates the diametertransition or discontinuity from the guidewire 110 to the distal tip 134of the dilator 120 of the prior-art. Currently available materials onlyallow for the wall thickness to be reduced to a certain level, belowwhich level the tip has insufficient strength and integrity.

FIG. 1B illustrates a prior-art assembly including a deformed dilator160 shown over guidewire 110. The distal tip 174 of dilator 160 has acrushed portion 184, as well as a flared portion 194. The tip of adilator may suffer many different types of deformation and may havetorn, buckled, crushed, flared and spindled regions. Such fraying causesadditional resistance to passage of the dilator through a tissue trackand into the puncture in a vessel wall because the frayed portionpresents more surface area to catch on the edges of the tissue track andthe puncture. In many instances, such fraying causes additional damage,even more tearing at the arteriotomy. The frayed dilator tears theartery to a greater extent than the discontinuity alone, as well asbeing more uncontrolled, as described above, and further exacerbates thecomplications noted above.

A numerical example will illustrate the foregoing description of aneedle, guidewire, and dilator of the prior art, and the manner in whichthe dilator tip engages the puncture hole in the vessel wall. The SDHtechnique for percutaneous entry into the femoral artery commonlyemploys an 18-gauge thin-wall needle for arterial puncture, throughwhich is inserted a close-fitting introducing guidewire with outerdiameter (“OD”) of 0.038-inch. The main body of the dilator isfrequently 6-French (˜0.079-inch outer diameter) for many procedures,but is most often in the range of 4-8 French but may be larger. Forchildren, the outer diameter may be as small as 2-French, and possiblyless for neonates. For the present we will use the example of a 6-Frenchdilator. From the main cylindrical outer body of the dilator, a shortdistal portion tapers conically down toward the outer diameter of theguidewire. However, the physical properties of flexible plasticstogether with limitations in manufacturing methods limit how thin a wallcan be achieved at the distal tip, resulting in a wall thickness of0.010-inch at the very distal tip of the dilator. To slide and advancefreely over the guidewire with a 0.038-inch outer diameter, the diameterof the opening at the tip of a 6-French dilator is approximately0.040-inch, the difference allowing for manufacturing tolerances andvariation of both the guidewire and dilator, and to avoid slidingfriction between dilator and guidewire. Therefore, the dilator tip withan opening having an inner diameter of 0.040-inch and wall thickness of0.010-inch at its distal tip will have an outer diameter of 0.060-inch,which is 58% greater than the 0.038-inch outer diameter of theguidewire. This represents a substantial relative increase in dimension,presenting an abrupt step which enters the femoral arteriotomy by bluntforce as this step-up in diameter engages and presses against thearterial wall. The entire blunt-step profile of the dilator tipsurrounding the guidewire enters the puncture hole at one instant as thearteriotomy tears open to accept the full diameter of the dilator tip.There is nothing to shield the perimeter of the puncture hole from beingassaulted with a dilator tip that is too large to be accepted into theexisting orifice. Often, the required force is considerable and thedilator tip generally “pops” through the puncture hole suddenly with apalpable abruptness. As this dilator tip penetrates the arteriotomy withbrute force it traumatizes and tears the arterial wall. This sameproblem also occurs during other medical procedures when a dilatorenters an opening that is smaller than its distal tip outer diameter.

In the numerical example described above, the inner diameter of theopening at the dilator tip was 0.040-inch. This is the inner diameter atthe tip area, but the bore diameter in the main body of the dilator maybe equal to or larger than 0.040-inch. During the manufacturing processwhen the tapered conical tip is created on the dilator, the opening atthe tip is reduced to the specified diameter, in this case 0.040-inch,at this same time.

Referring now to FIGS. 2A-2C, the SDH Technique of the percutaneousprocedure is performed in the following manner. As shown in FIG. 2A, aneedle 205, having hub 206 and tip 207 penetrates the skin 220,traverses the subcutaneous tissue 230 and other soft interveningstructures, creating the initial tissue track, and punctures the vesselwall 240. Its tip 207 enters the lumen 250 of blood vessel 270 creatingpuncture hole 245. A guidewire 110 is inserted through the hollow boreof needle 205 and into the vessel lumen 250. Once the guidewire 110 issecurely in place, the needle 205 is removed, leaving guidewire 110 inplace extending from outside skin 220 to inside lumen 250. Blood mayflow out of the puncture 245 in vessel wall 240 but the presence ofguidewire 110 in the puncture hole tends to minimize the leakage ofblood.

A dilator 280 carrying a sheath 290 is then advanced over the guidewire110, through skin 220 and subcutaneous tissue 230 along the tissue trackto the wall 240 of blood vessel 270. FIG. 2B shows an enlarged view ofthe distal end of the dilator 280 approaching the puncture hole 245,previously created by the needle, in wall 240. As can be appreciated bythe skilled artisan, the significant difference in diameter between theouter diameter of the guidewire OD1 and the outer diameter OD2 of thedilator's distal tip 284 causes resistance to further advancement of thedilator, resulting in trauma to the vessel wall 240 as the dilator'sdistal tip 284 penetrates the vessel wall 240 through the smallerpuncture hole 245, particularly when the arterial wall of the puncturehole is snugly fitting around the guidewire 110.

The difference in diameter from guidewire 110 to distal tip 284 of thedilator 280 necessitates that additional force be exerted by thepractitioner to advance tip 284 along the tissue track through one ormore of skin 220, tissue 230 and vessel wall 240. The blunt end of tip284 effectively focuses the force applied by the practitioner todisplace or tear through the several layers. As shown in FIG. 2C, thebluntness of tip 284 meets substantial resistance to its entry into thepuncture hole 245 in wall 240 of the blood vessel, particularly inmuscular arteries. The enlarged view within FIG. 2C shows thedeformation of the vessel wall by the dilator tip 284 as it attempts toenter the smaller diameter puncture hole 245, through which theguidewire 110 extends. Therefore, the practitioner must increase theforce he exerts on the dilator in order to overcome this resistance. Thevessel wall finally yields, traumatically, by tearing and accepts thefull diameter of tip 284. The practitioner feels a palpable “pop”sensation as the vessel wall tears around the puncture hole 245. Inaddition, upon penetrating vessel wall 240, the sudden reduction inresistance frequently causes the dilator to lurch forward, pushingdilator 280 uncontrollably into the lumen 250, and may result in distaltip 284 of dilator 280 striking opposite wall 260 of vessel 270 andcausing a damaging abrasion. Similar resistance is encountered in othermedical procedures when a dilator is advanced to and through an openingin an anatomic structure that is smaller than the outer diameter of thedistal tip of the dilator.

In the percutaneous technique, the dilator 280 carries sheath 290. Thedilator-sheath assembly is then advanced through the vascular wall 240until the sheath's distal portion resides in the vessel lumen 250. Thedilator and guidewire are then removed, leaving a channel of the desiredFrench-size into the vessel via the thin-walled sheath. Theoperator/surgeon is now able to insert via the sheath a diagnostic ortherapeutic catheter, or other devices.

FIG. 3A is a top view of blood vessel 270 after it has been punctured bya beveled needle of the prior art, illustrating the typicalcurvilinear-shaped slit of puncture 310 in vessel wall 240 created bybeveled tip 207 of needle 205. The angle of the bevel, the orientationof the bevel as it engages vessel wall 240, and the angle at which theneedle approaches vessel wall 240, create a curvilinear-shaped slitpuncture 310, not a circular-shaped puncture.

FIG. 3B is a top view of vessel 270 after it has been punctured by abeveled needle and dilated by dilator 280 of the prior art. After needle205 creates an initial puncture, guidewire 110 is inserted through thebore of needle 205 and into lumen 250 of vessel 270. Needle 205 isslidably removed keeping guidewire 110 in place. Dilator 280 is advancedover guidewire 110 to vessel 270. When distal tip 284 of dilator 280reaches vessel wall 240, at least a portion of tip 284 impacts vesselwall 240 causing the wall to deform. When the deformation of vessel wall240 reaches its elastic limit, the wall tears, causing a palpable “pop”sensation. The tearing may occur in one or more places along puncture320 but generally occurs at the ends of the puncture, as shown by tornregions 330 and 340. As a result of the tearing and dilation, puncture320 is much wider than the original puncture 310 and more irregular.

The tearing caused by dilator 280 is worse if tip 284 frays or isotherwise deformed before reaching vessel wall 240. As the exposed tip284 of the dilator is advanced through the tissue track, the resistanceof tissue 230 often causes tip 284 to fray or to be otherwise deformed.

FIG. 3C is a top view of blood vessel 270 after it has been punctured bya beveled needle and dilated by prior-art dilator 160 having a frayeddistal tip 174. An initial, curvilinear puncture 310 is created byneedle 205. Guidewire 110 is then deployed into lumen 250 of bloodvessel 270. As dilator 160 passes through skin 220 and subcutaneoustissue 230, tip 174 of dilator 160 deforms and frays in a similarfashion as depicted previously at tip 184 and tip 194. When frayed tip174 reaches vessel wall 240, it presents a more irregular surfaceagainst vessel wall 240 than would an unfrayed tip, and the operatorfeels increased resistance compared to an unfrayed tip. Vessel wall 240deforms as frayed distal tip 174 is advanced, and finally vessel wall240 tears in an uncontrolled manner. The resulting tearing is morepronounced and varied than that caused by the unfrayed dilator tip 130,as shown at torn regions 360, 370 and 380. Torn regions 360 and 380 atthe ends of puncture 350 are more extensive than torn regions 330 and340. As a result of the extensive tearing and dilation, puncture 350 islarger than puncture 320 and much larger than needle puncture 310.

The tearing of the vessel wall and trauma caused to the surroundingareas by the deformed or frayed tip of the dilator are significantproblems for the patient. Such damage results in more lengthy anddifficult hemostasis at the conclusion of the invasive procedure. Also,a hematoma and other complications are more likely to occur.

As illustrated above, there are deficiencies with the current tools usedfor the percutaneous technique, particularly the SDH technique. Oneproblem is caused by the discrete step-like increase in diameter fromguidewire to dilator tip. This increase in diameter is a principalfactor determining the force which must be exerted by the dilator tip ontissue during passage along the tissue track and causes the resistanceto entry of the dilator tip into the arteriotomy in the muscular wall ofthe blood vessel. The operator experiences this noticeable resistance asthe blunt leading face of the dilator tip tries to pass through thearteriotomy which is too small to easily accept it.

Another problem encountered in the prior art is that the exposed andunprotected tip of the dilator often becomes frayed as it passes throughthe tissue track. Such fraying will be cause for additional resistanceto entry of the dilator tip into the arteriotomy, as the frayed portioncatches on the edge of the arteriotomy impeding passage of the dilator,and creating a larger tear.

Yet another problem encountered is the trauma and tearing of thearterial wall as the blunt dilator tip passes through it. This resultsin more lengthy and difficult hemostasis at the conclusion of theinterventional procedure when all devices are removed from the patient.The size of the post-procedural puncture hole in the blood vessel wallcorrelates to post-procedural bleeding, time to hemostasis, hematomaformation, and other complications.

Thus, there is a need for a medical filament that eliminates orsubstantially reduces the abrupt transition or step-up between thefilament and a dilator's tip when the dilator is introduced togetherwith and over the filament into a patient, thereby providing smoothdilation of the target orifice. It would be desirable to provide amedical filament that reduces the damage to tissue or blood vessel wallwhen the dilator is introduced. It would be particularly useful tointroduce such a filament and a filament-and-dilator combination adaptedfor use in the SDH technique.

Objects of the Invention

Accordingly, it is an object of the invention to provide an improvedintroducing filament to facilitate insertion of a dilator bypercutaneous techniques for vascular access, and thereby remedy thedeficiencies of the prior art.

It is also an object of the invention to provide apparatus and methodsto facilitate insertion of a dilator by percutaneous techniques forvascular access and for accessing other anatomic structures.

It is another object of the invention to reduce or eliminate the step-upin diameter from the introducing guidewire to the distal tip of thedilator.

It is yet another and related object of the invention to reduce oreliminate resistance to advancement of the tip of the dilator throughtissues, the tissue track, and into the wall of a blood vessel or intoother anatomic structures.

It is yet another object of the invention to reduce or eliminate theuncontrolled entry and its associated trauma, accompanied by thepalpable “pop” sensation, as the tip of the dilator overcomes theresistance of the target orifice to insertion.

It is still another object of the invention to reduce or eliminate thefraying and deformation suffered by the tip of the dilator as it ispassed through a tissue track to the target orifice, and to reduce oreliminate the additional resistance caused by a frayed or deformed tipas it enters into the target orifice.

It is yet another object of the invention to provide a dilator having adistal tip whose outer diameter is smaller than the outer diameters ofthe distal tips of known dilators used for comparably-sized guidewires,without sacrificing the structural integrity of the tip, in order topermit the size of initial puncture holes to be reduced.

It is another object of the invention to provide a dilator having adistal tip whose outer diameter is both smaller than the outer diameterof the needle used and smaller than the target orifice created by thepuncturing needle.

It is still another and related object of the invention to reduce oreliminate blood backflow through the needle bore resulting from thepuncture of the blood vessel by the needle.

It is yet another object of the invention to reduce or eliminate bloodbackflow from the puncture site around the guidewire, while at the sametime reducing or eliminating the step-up in diameter from theintroducing guidewire to the tip of the dilator.

It is yet another object of the invention to reduce the force that apractitioner must exert to insert the tip of the dilator during passageof the dilator along a tissue track, and to reduce the force exerted bythe tip of the dilator on the tissue track and the wall of the bloodvessel.

It is a further object of the invention to reduce or eliminate trauma,or tearing of a blood vessel wall or other anatomic structure when thetip of a dilator is introduced through the puncture.

It is yet another object of the invention to provide a kit of componentsincluding a needle, guide element and dilator where the shielding of thedilator tip allows it to be fabricated in the smallest of sizes toaccess blood vessels and target orifices, as is needed in pediatric andneonatal procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

Several exemplary embodiments of the invention are described below.However, it is to be understood that the invention is not limited to thedetails of construction or processes set forth in the followingdescription and drawings. The invention is capable of other embodimentsand of being practiced or executed in various ways. The drawings are notnecessarily drawn to scale, and certain features have been enlarged todepict geometric aspects and relations between features of the variousembodiments of the invention. As such, the relative size of variousfeatures of embodiments of the invention may be enlarged with respect toother features of the device or parts of the body shown in the drawings.

FIGS. 1A and 1B show a partial longitudinal section of a prior-artguidewire and dilator assembly.

FIG. 2A shows a needle whose tip has been inserted into a patient'sblood vessel and a prior-art guidewire residing within the needleaccording to the SDH technique.

FIG. 2B shows a prior-art guidewire within a patient's blood vesselafter the needle has been removed, leaving the guidewire in place withits distal portion residing in the blood vessel, and the dilator withaccompanying sheath passing over the proximal end of said guidewire.

FIG. 2C shows a prior-art guidewire and dilator combination with thedistal tip of the dilator engaging the puncture hole in the blood vesselwall created by the needle.

FIG. 3A illustrates a puncture in a vessel caused by insertion of abeveled needle according to the prior-art SDH technique.

FIGS. 3B and 3C illustrate a torn, traumatized puncture in a vesselcaused by insertion of a dilator over a guidewire according to theprior-art SDH technique.

FIG. 3D illustrates a puncture caused by insertion of a dilator andguidewire according to an embodiment of the invention.

FIG. 4A shows a longitudinal-sectional view of a filament according to afirst embodiment of the invention.

FIG. 4B shows a longitudinal cross-sectional view of a filament in theform of a guidewire according to an embodiment of the invention.

FIG. 5A shows a close-up longitudinal-sectional view of the preferredembodiment of a filament and dilator combination of the inventiondepicting the exact-shielding of the dilator tip.

FIG. 5B shows a close-up longitudinal-sectional view of an alternateembodiment of a filament and dilator combination of the inventiondepicting the exact-shielding of the dilator tip.

FIG. 5C shows a longitudinal-sectional view of a second embodiment of afilament and dilator combination of the invention depicting theover-shielding of the dilator tip.

FIG. 5D shows a longitudinal-sectional view of a third embodiment of afilament and dilator combination of the invention depicting thepartial-shielding of the dilator tip.

FIG. 5E shows a longitudinal-sectional view of an alternate embodimentof a filament and dilator combination of the invention depicting thepartial-shielding of the dilator tip.

FIG. 6A shows an embodiment of the filament of the invention in useduring the percutaneous technique with the filament residing in thehollow bore needle that has been inserted into a blood vessel.

FIG. 6B shows the use of the filament of FIG. 6A in place with a distalportion residing within a blood vessel, and the dilator, withaccompanying sheath, being slidably advanced over the proximal end ofthe filament. The dilator tip is shown approaching the filament'sannular step transition.

FIG. 6C shows the filament of FIGS. 6A-6B with the dilator tip abuttingthe annular step transition of the filament as the dilator's tip engagesthe puncture hole in the blood vessel wall.

FIGS. 7A-7C show several elements for use at the filament's annular steptransition to facilitate shielding of the dilator tip.

FIGS. 8A-8C show several elements for use at the filament's annular steptransition to more precisely center the dilator on the filament.

FIGS. 9A-9B illustrate filament-dilator coupling mechanisms according toembodiments of the invention.

SUMMARY OF THE INVENTION

The applicants have developed novel apparatus and methods that aresignificant improvements over the instruments and procedures previouslyutilized to implement the SDH technique. They may be advantageously usedto access other anatomic structures having passages or hollow cavitiessuch as a kidney, lung, esophagus, pleural cavity, rib cage, cyst orabscess that contains liquid or gas.

Embodiments of the present invention pertain to eliminating, or at leastreducing, the step-up or discrete transition from the outer diameter ofthe prior-art introducing guidewire to the outer diameter of the dilatortip. The inventive filament reduces or prevents trauma to the bloodvessel as the combination of these two devices is insertedlongitudinally through the tissue track of a patient and into anarteriotomy in a blood vessel. In prior art devices, the discretestep-like increase in diameter from the filament or guidewire to thedilator tip is the principal factor which creates the resistance toentry of the dilator tip into the tissue, and the major cause of traumaand tearing of the arterial wall during procedures involving access toarteries, and as such also results in more lengthy and difficulthemostasis at the conclusion of the procedure when all implements areremoved from the patient.

Embodiments of the present invention also create a better match betweenthe diameter of the leading tip of the dilator engaging the vessel wallas the tip more closely approximates the outer diameter of the existingpuncture hole, or opening, as created by the puncturing needle, andideally fits within the perimeter of the existing puncture hole. In apreferred embodiment, this is best accomplished via a mating regionbetween the inventive filament and dilator distal tip with little or nodiameter difference, and therefore no step-up between the respectiveouter diameters of filament distal segment and dilator tip.

The invention is an elongate introducing guide element, or filament,having proximal and distal segments which, at their juncture, form anabrupt, annular, circumferential step transition, the outer diameter ofthe distal segment adjacent said step being greater than the outerdiameter of the proximal segment adjacent said step. The abrupt diameterchange creates a proximally-facing circumferential surface at the steptransition, which is the proximally-facing end of the distal segment.The outer diameter of the distal segment at the step is also greaterthan the inner diameter of the mating dilator's opening at its distaltip so that the dilator cannot advance beyond the step, and the tip ofthe dilator is shielded behind the abrupt circumferential step. Thedistal segment of the guide element is, or has a portion that is, ofsufficient diameter and length to block blood flow through the needlewhen it is situated inside the bore of the needle, and to block bloodflow through the puncture hole after the needle has been removed.

As can be appreciated, the increase in diameter from the guide elementto the tip of the dilator in prior-art systems is eliminated. As theguide element and dilator of the invention are advanced together, theguide element effectively shields the tip of the dilator from beingabraded or impacted by the tissue along the track leading to the targetorifice. The circumferential step also shields the distal tip from theedges of the puncture. When the outer diameters of the tip of thedilator and the step match closely there is a smooth transition from theguide element's distal segment to the dilator's distal tip. This permitsthe tip and conical portion of the dilator to smoothly enter and dilatea puncture site in an elastic vessel without resistance from the targetorifice and without abrupt tearing of the vessel wall.

A further advantage of the step transition is that the diameter of theproximal segment of the introducing filament is reduced relative toprior-art filaments, which in turn permits the lumen of the dilator tobe reduced since it now passes over a filament with a smaller diameter.The wall thickness at the dilator distal tip can now also be reducedsince it will now be shielded by the step and not subject to fraying anddeformation as are the exposed dilator tips of the prior-art. Thereduced dilator lumen and reduced wall thickness of the dilator tippermits the dilator tip outer diameter to be significantly reducedrelative to prior-art dilators. This allows the initial puncture hole tobe made smaller, since it now needs to accommodate a smaller dilatortip, yet still be dilated to the desired size by the dilator. Thediameter of the puncturing needle can now also be reduced. The foregoingshows that dilator tips, as well as the entire associated system ofcomponents, can now be fabricated in miniaturized sizes not presentlyavailable. This is of particular value in pediatric and neonatalprocedures where smaller sizes of tools are of paramount importancegiven the small sizes of the blood vessels being accessed.

Using the apparatus of the preferred embodiment of the invention, asmooth transition between the guide element distal segment and the tipof the dilator is achieved. By utilizing a mating dilator with an outerdiameter at its distal tip that is equal or nearly equal to the outerdiameter of the distal segment of the guide element adjacent the step,the matching outer diameters provide “equal-shielding” and ensure asmooth transition from the distal segment of the guide element to thetip of the dilator.

According to a second embodiment, the tip of the mating dilator has asmaller outer diameter than the diameter of the distal segment of theguide element at the step. When the two are advanced together distally,the step in the guide element effectively over-shields the distal tip ofthe dilator. According to a third embodiment, the tip of the dilator hasa slightly larger outer diameter than the outer diameter of guideelement distal segment adjacent the step. As the dilator and guideelement are advanced distally together along the tissue track to andthrough the target orifice, at least a portion of the thickness of thewall of the distal tip is shielded by the step. This partial shieldingallows for a substantial reduction of the increase in diameter fromguide element to the tip of the dilator as compared to prior artsystems, while still protecting a significant portion of the dilatortip.

The elimination of resistance encountered by the tip of the dilator,whether equally-shielded or over-shielded, prevents both damage to thetip of the dilator and trauma to the tissue track and target orifice.The reduction of resistance encountered by the tip of the dilator whenpartially-shielded provides a similar benefit.

Preferably, the shape or contour of the tip of the dilator which abutsthe step and the shape of the proximally-facing surface of the step arecomplementary, so that they abut in a contiguous contoured manner. In analternate embodiment, the tip of the dilator mates or interdigitateswith the proximally-facing surface of the step to enhance the matingcontact between the dilator tip and the step transition.

The dimensions of the guide element and the dilator are well known tothose skilled in the art. By way of example, the outer diameter of thedistal segment of the guide element may be from 0.010 to 0.053 inches tomatch the respective bores for the range of needles used forpercutaneous entry, and be from 0.006 to 0.047 inches larger than theouter diameter of the proximal segment of the guide element adjacent thestep. The circumferential step has a proximally facing surface, which isthe end surface at the proximal end of the distal segment. The plane ofthat surface is preferably perpendicular to the longitudinal axis of theproximal segment of the guide element, but may be angled proximallybetween 60 to 90 degrees to the central and longitudinal axis of theproximal segment of the elongate guide element. The maximum outerdiameter of the dilator may typically range up to 9 French for themajority of contemporary procedures.

The inventions also include kits. Such kits typically include a needleor other hollow device having a sharp distal tip; an elongate guideelement; and a dilator. The kits may also include sheaths.

The inventions also include methods for creating and dilating an openingin the wall of a blood vessel or other anatomical structure. The methodis a modification of the SDH technique that includes serial stepsstarting with inserting a needle, or other sharp tubular device, intothe wall of the blood vessel to create the opening. The next step isinserting an elongate guide element of the present invention into theinternal bore of the needle or tubular device. The distal segment of theguide element is of sufficient length and diameter to substantiallyreduce the flow of blood through the internal bore of the needle. A partof the distal segment extends beyond the distal tip of the needle, andtherefore extends through the opening in the wall of the blood vesseland into the lumen of the vessel. Preferably the circumferential step islocated proximal to the needle hub so that it can be seen and felt bythe operator. However, it may optionally reside within the needle boreat any point outside the blood vessel, preferably at a point above skinlevel. The needle is then slidably removed from the blood vessel whilekeeping the distal segment of the elongate guide element in the lumen ofthe blood vessel and the circumferential step outside the blood vessel.

In the next step, a dilator is slid over the proximal segment of theguide element. The dilator has an interior passage of sufficient size topass over the maximum outer diameter of the proximal segment of theguide element, but not large enough to pass over and beyond thecircumferential step. The dilator has a tapered distal end with a distaltip whose outer diameter preferably is not greater than the outerdiameter of the distal segment of the guide element at the step. Themain body of the dilator has a maximum outer diameter greater than theouter diameter of the distal segment of the elongate element so that itcan perform its function of dilating the target opening. The dilator isthen advanced along the proximal segment until its distal tip abuts theguide element's circumferential step. Then the elongate guide elementand the dilator are advanced together through the opening whilemaintaining the dilator tip in firm contact with the circumferentialstep to shield it from intervening tissue and the edges of the opening.The dilator is then advanced farther into the opening to dilate it.

The opening to be dilated need not be created by a needle to benefitfrom the smooth transition between guide element and dilator provided bythe invention. Naturally-occurring openings or portions of an existingpassage may be dilated more smoothly with the apparatus of theinvention. Alternatively, openings can be created, for example, bycannulas and other tubular instruments, simple incisions, traumaticinjury, and the like. Guide elements of the present inventions mayinclude guidewires and other types of filaments

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of a filament according to the present invention isshown in FIG. 4A. Filament 400 includes a proximal segment 405 and adistal segment 415 which at their juncture form an abrupt,circumferential step 410. Segments 405 and 415 may have the same ordifferent configurations, but cylindrical configurations are preferredfor both segments. Distal segment 415 serves multiple purposes: At itsproximal end, it forms the abrupt step 410 which shields the distal tipof a dilator; its one or more regions of maximum diameter also block thebackflow of blood through the needle, and also block the backflow ofblood through the vessel puncture.

Proximal segment 405 has a maximum outer diameter 425 that is preferablysubstantially constant along the length of proximal segment 405. Distalsegment 415 includes tip 420 and a cylindrical elongate portion 440having a maximum outer diameter 430 that is preferably substantiallyconstant along the length of cylindrical elongate portion 440. At step410 the distal outer diameter 430, typically in the range of 0.010 to0.053 inches, is larger than proximal outer diameter 425, typically inthe range of 0.006 to 0.047 inches, creating the annular circumferentialstep. Outer diameter 430 is closely matched to the diameter of the boreof the needle with which filament 400 will be used, and when therespective diameters are properly matched, cylindrical elongate portion440 will substantially block the backflow of blood from the vesselthrough the needle bore. Those skilled in the art are familiar withhollow bore needles and matching filaments. Needles for percutaneousentry are typically in the range of 17 g-21 g for adults and 21 g-25 gfor pediatrics, and have a corresponding bore of a diameter in the rangeof 0.012 to 0.057 inches. In the future, the lower end of the range maydecrease further as devices are made smaller.

The length of cylindrical elongate portion 440 is broadly from 30 mm,for pediatric uses, to 300 mm. In preferred embodiments, portion 440 isfrom 70 mm to 150 mm long. Cylindrical elongate portion 440 should besufficiently long so that at least a significant length, e.g. 20 mm foradult use, can extend from the puncture site into the blood vessel,thereby reducing the backflow of blood from the puncture into the tissuetrack, and a second length, e.g. 70 mm in adult use, can extend throughthe bore of the needle. A further additional length, e.g. 30 mm, mayextend proximally from the proximal hub of the needle. Cylindricalelongate portion 440 thus serves a shielding-and-blocking function.First, it blocks the backflow of blood through the needle. Second, itsubsequently blocks the backflow of blood through the puncture site.Third, it shields the tip of the dilator. Outer diameter 430 preferablyremains constant along the length of portion 440 but may vary providedthat portion 440 has an appropriate diameter or diameters along itslength to perform its blood-blocking functions. Tip 420 is the leadingpart of distal segment 415. It may have a curved distal end portionresembling the letter “J,” commonly referred to as a “J-tip,” whoselength may generally range from 2 cm to 5 cm.

The total length of filament 400 is preferably 600 mm or less. The totallength of the filament of the invention is determined by the combinedlengths of the portions of the filament residing in the lumen of theblood vessel, within the needle for its entire length, and outside theneedle hub. In an obese patient with a large skin-to-artery distance,the filament would need to be longer. For pediatrics it would be made ina shorter length.

The change in diameter at the juncture of proximal segment 405 anddistal segment 415 forms circumferential annular step 410. Preferably,circumferential step 410 is a substantially discrete, abrupt, annularstep-down from the larger diameter of distal segment 415 to the smallerdiameter of proximal segment 405. Step 410 creates the annular,proximally-facing end-surface 435 which shields the tip of a dilator.The term “proximally-facing” means that the end surface is orientedtoward or substantially toward the proximal end of the guide element.The end-surface of step 410 may be perpendicular to the longitudinalaxis of the guide element or may be angled to that axis, and may haveportions that are not strictly perpendicular to that axis. Theend-surface, or portions thereof, may be angled between 60-90 degreesfrom the longitudinal axis and still be considered proximally-facing.

Surface 435 of step 410 may be angled proximally or distally at 60 to 90degrees to the longitudinal axis of the guide element. The angledescribed is that subtended from the longitudinal axis of the proximalsegment to surface 435. At angles of less than 90 degrees,proximally-facing surface 435 may have a region with an inwardly conicalshape (i.e., a concavity), which captures the tip of a dilator.Alternatively, surface 435 may have an outwardly conical surface whichmates with the distal-tip opening of the dilator. Surface 435 may havevarious planes and shapes provided that it effectively stops the distalmovement of an advancing dilator when the dilator abuts the former.

In a preferred embodiment, proximally-facing surface 435 is an annular,ring-shaped, substantially flat surface. Most preferably,proximally-facing surface 435 is geometrically complementary orsubstantially complementary to the distal surface of the tip of adilator.

Proximal segment 405 and distal segment 415 may each be made of metal,thermoplastic, composite material or other relatively strong butflexible material, chosen to confer mechanical properties on distalsegment 415 which permit it to pass through a hollow-bore needle into avessel, and to flex to follow the path of the vessel. Manufacturingmethods and materials to achieve this purpose are well known in the art.Distal segment 415 may advantageously include a lubricious coating tofacilitate its navigation through the bore of a needle and through avessel.

FIG. 4B illustrates a preferred embodiment of filament 400 in the formof a stepped introducing guidewire 450. Stepped guidewire 450 includes aproximal segment 455 and a distal segment 465 which at their junctureform circumferential step 460. The total length of guidewire 450 ispreferably 600 mm or less. Proximal segment 455 has an outer diameter475 which preferably is substantially constant along its length. Theproximal end of distal segment 465 creates step 460 to shield the tip ofa dilator. Distal segment 465 also serves to block the backflow of bloodthrough a needle from a vessel puncture.

The term guidewire suggests that it is made from metal (based on theword “wire”), as guidewires currently are. However, with manufacturingadvances a guidewire may take on different forms in the future. Forexample, it may be made entirely from thermoplastic or another type ofmaterial that may not normally be considered materials from which tomake a wire. Or it may be made from a combination of materials, such asmetal and a material such as a thermoplastic material. Structurally, itmay be made from a unitary piece of material. Similarly, “core wire”, asknown in present day guidewire construction, or “core section”, may bemade from thermoplastic or another material. Thus, it will be understoodthat alternate embodiments of the filament or guide element can beachieved through the use of various materials other than metal. The termguidewire is used herein to denote any guiding element with the physicalproperties detailed in this application regardless of the material ofwhich it is made.

As shown in FIG. 4B, proximal segment 455 is advantageously formed fromcore wire 458, which is a solid wire that extends the length ofguidewire 450. Core wire 458 is preferably made of metal, plastic,composite material, or other relatively strong but flexible material sothat distal segment 465 can be passed through a hollow needle into avessel and can flex to follow the path of the vessel. Core wire 458 maycomprise a tapered distal end portion 472.

Distal segment 465 has tip 470 and a cylindrical portion 490 withdimensions as described above for distal segment 415 of FIG. 4A. Itsfunctions and characteristics are as described in connection with distalsegment 415. Distal segment 465 may include regions of varyingflexibility.

As shown in FIG. 4B, distal portion 490 is advantageously formed fromcoil wire 464 spirally wrapped around core wire 458. Coil wire 464 ispreferably made of a flexible material comprised of metal, thermoplasticor composite. Coil wire 464 is most preferably made of a flexible metalhaving some shape retention qualities and may possess a lubricioussurface to facilitate passage through a needle bore and navigationthrough a blood vessel. Tip 470 may be formed by a hemispherical cap494. Coil wire 464 may be replaced with a sleeve of suitable material,which may incorporate tip 470. The change in diameter at the junction ofproximal segment 455 and distal segment 465 is as described inconnection with FIG. 4A, and creates proximally-facing annularend-surface 485, whose functions and characteristics are as describedabove in connection with proximally-facing surface 435.

In a preferred embodiment, proximally-facing surface 485 of distalsegment 465 is a circumferential, ring-like, annulus, with at least aportion of its proximally-facing surface that is substantially flat. Theflat surface may be created by various means, for example, by machininga flat surface into the last helical loop 462 of coil wire 464. If adiscontinuity in the ring shape naturally results it may be welded orotherwise filled with a suitable material. Alternatively, surface 485may comprise a single helical loop of coil wire 464. As furtheralternatives, surface 485 may be provided with an additional structuralelement to create the proximally-facing surface, such as a circulardisc, similar to a washer, to provide a flat surface, or an externallycylindrical section with an inwardly conical-shaped interior, or acup-shaped piece, a radiographic marker band, radio-opaque element, orthe like. FIG. 4B shows surface 485 drawn with a half-coil of lasthelical loop 462 on the upper side.

FIGS. 5A-5C depicts longitudinal sectional views of assemblies of afilament of the invention and a mating dilator in cooperatingrelationship. FIG. 5A is a longitudinal cross-sectional view of thecombination 500 of a dilator 505 and filament 510 in cooperatingrelationship. FIG. 5A shows the preferred embodiment which providesequal shielding of the dilator tip 507. The proximal segment 520 offilament 510 is shown fully inserted into dilator 505 so that the distaltip 507 of dilator 505 in an abutting relationship with circumferentialstep 525. The outer diameter of the tip of dilator 505 matches the outerdiameter of distal segment 515 of filament 510 at step 525. Whenadvanced together distally into the patient, distal segment 515 shieldsthe tip 507 of dilator 505, eliminating any discontinuity betweenfilament 510 and the tip 507 of dilator 505, and thereby facilitating asmooth insertion and passage of the dilator and filament combination 500into a pre-existing puncture hole or orifice.

In this preferred embodiment, the lack of a diameter transition from theouter diameter of the distal segment of the filament to the distal tipof the dilator allows the filament distal segment to fully shield thedilator's distal tip surface. This reduces trauma when inserting thedilator in combination with the filament into a target orifice. Theshielded tip of the dilator traverses the tissue track and the targetorifice without the resistance experienced with the apparatus of theprior art.

In the preferred embodiment the dilator's increasing taper begins at thedistal tip. In alternate embodiments the dilator has an intermediatecylindrical segment between the distal tip and the beginning of thetapered segment. As shown in FIG. 5B, dilator 505B includes cylindricalsegment 506 between distal tip 507B and tapered segment 508B.

FIG. 5C is a longitudinal sectional view of the combination 530 of adilator 535 and filament 540 in cooperating relationship to provideover-shielding of the tip 537 of dilator 535. At the circumferentialstep 555, the outer diameter of the tip 537 of dilator 535 is smallerthan the outer diameter of the distal segment 545 at step 555. Moving inthe proximal direction along distal segment 545 to dilator 535, there isa circumferential step down from the outer diameter of distal segment545 to the outer diameter of the tip 537 of dilator 535. Advancedtogether distally, the filament's distal segment 545 over-shields thetip 537 of dilator 535. In this embodiment the outer diameter of thedistal segment of the filament provides an excessive shield orover-shield for the distal tip. As compared to the guidewire and dilatorof the prior art, this embodiment eliminates trauma when inserting adilator tip in combination with the filament into a target orifice.

FIG. 5D is a longitudinal sectional view of the combination 560 of adilator 565 with filament 570 in cooperating relationship to providepartial shielding of the distal tip of dilator 565. The outer diameterof the tip of dilator 565 is larger than the outer diameter of thedistal segment 575 of filament 570 at the circumferential step 585, butthe inner diameter of the tip of dilator 565 is less than the diameterof distal segment 575 at the step. Therefore the distal tip 577 ofdilator 565 is partially shielded by distal segment 575. As compared tothe prior-art, this partial-shielding also reduces trauma as the dilatorand filament of combination 560 passes through tissue and enters into atarget orifice.

As a non-limiting example, a filament with a distal segment of0.038-inch diameter is compared to a prior-art guidewire with a0.038-inch diameter. The dilator tip outer diameter is 0.044-inch, whichis less than the diameter of a prior art dilator used with a 0.038-inchguidewire, and the tip inner diameter is 0.024-inch. The wall thicknessis thus 0.010-inch at the tip. The filament proximal segment has anouter diameter of 0.022-inch to match the dilator's distal tip openingof 0.024-inch. The distal segment outer diameter is 0.038-inch, a commonsize in the SDH technique. Thus, the annular step on theproximally-facing surface of the distal segment of the filament is0.008-inch in width, which is half of the difference between 0.022-inchand 0.038-inch. As compared to the prior art, in which the dilator'sleading tip is 100% exposed (i.e. 0% shielded), the 0.038-inch diameterannular step of the filament shields 86% of the 0.044-inch diameterdilator tip. Although dilator tip 577 is not completely shielded, thisis still a significant improvement over prior-art devices. As can beseen from this example, the dilator leading tip is 86% shielded, ascompared to 0% shielding for the prior-art device, and, the outsidediameter of the dilator's distal tip is reduced to 0.44-inch as comparedto 0.060-inch as described above in paragraph 19 for a comparably sizedguidewire 0.038-inch in diameter. This demonstrates that the inventionachieves the very important objective of reducing the size of initialpuncture holes.

In certain embodiments, the tip of the dilator may have a chamfered orrounded outer annular edge. In FIG. 5E, dilator tip 577E of dilator 565Ehas a chamfered outer annular edge 579, providing a smoother transitionfrom filament to dilator tip.

FIGS. 6A-6C illustrates the use of an embodiment of the invention. Theimproved SDH technique of the invention includes the steps ofpenetrating skin 220 with a needle 205, traversing subcutaneous tissue230 and puncturing wall 240 of blood vessel 270 such that the needle tip207 lies within the lumen 250 of the blood vessel to provide access tothe lumen. Backflow of blood from the vessel through the bore of theneedle verifies placement of the needle. Filament 510 is then insertedinto the needle hub and advanced through the needle and into lumen 250.

In FIG. 6A filament 510 is positioned such that at least a part ofdistal segment 515 of filament 510 is positioned in lumen 250 and atleast a part is positioned in the bore of the needle 205; at least apart of the proximal segment of filament 510 extends out of the hub ofthe needle. The circumferential step 525 of filament 510 is preferablypositioned proximal to the needle hub so that it can be seen and felt bythe operator. However, it may also reside in the needle bore at anypoint outside the blood vessel, preferably at a point above skin level.In all cases, distal segment 515 substantially fills the inner bore ofthe needle to prevent the backflow of blood through the bore of theneedle. Once filament 510 is in place, the needle is slidably removedover filament 510 without substantially changing the position of thefilament.

FIG. 6B depicts the filament positioned in the blood vessel andextending above the skin. In the preferred embodiment, circumferentialstep 525 is above the skin. The proximal end of filament 510 is theninserted into the longitudinal inner bore of dilator 505. Dilator 505preferably carries a sheath 290 on the exterior of its main body.Dilator 505 is advanced over the proximal segment of filament 510 untilthe distal tip 507 abuts the proximally-facing surface ofcircumferential step 525. The enlarged view within FIG. 6B depictsdistal tip 507 approaching step 525. It shows the preferred embodimentin which the two components have matching diameters and thereforeprovide equal shielding of tip 507. When tip 507 abuts step 525, dilator505 and filament 510 are advanced together in abutting relationshipthrough skin 220 and subcutaneous tissue 230 to wall 240 of blood vessel270.

If circumferential step 525 is positioned at or below skin 220, dilator505 is advanced over the proximal segment of filament 510 until itfirmly abuts the proximally-facing surface of step 525. Filament 510 anddilator 505 are then advanced distally together in an abuttingrelationship to vessel wall 240.

FIG. 6C illustrates the preferred embodiment where the outer diameter ofthe filament's distal segment 515 at step 525 and the outer diameter ofthe tip 507 of dilator 505 are substantially equal, providing a smoothtransition from filament to dilator while filament and dilator are inabutting relationship. It can be appreciated that this smooth transitioneliminates trauma to the tip of the dilator and to the walls of thetissue track. Due to the equal shielding of the tip 507 bycircumferential step 525 of filament 510, the tip 507 of dilator 505penetrates the vessel wall 240 through the puncture previously createdby the needle without localized trauma or distension of the vessel wallat the moment of initial entry of the dilator tip into and through thepuncture 245. Desirably, the transition between filament and dilator issmooth such that no palpable “pop” sensation is felt by the operator asthe dilator first enters the puncture.

As dilator 505 is advanced farther, the conical taper of the dilator'sdistal portion smoothly dilates puncture 245 to accommodate the largerouter diameter of the main body of dilator 505. Sheath 290 is thenadvanced in tandem with dilator 505 through skin 220, tissue 230 andvascular wall 240 until a distal portion of sheath 290 is located wellwithin vessel lumen 250. The filament 510 and dilator 505 are thenremoved, leaving sheath 290 in place to provide an open channel to lumen250. A practitioner may then insert a diagnostic or therapeutic catheteror other devices into vessel lumen 250 via sheath 290.

FIG. 3D is a top view of the resulting opening 390 in blood vessel 270after it is punctured by a beveled needle and dilated by dilator 505which has been fully shielded by step 525. As can be appreciated in FIG.6C, as the tapered portion of dilator 505 is advanced into and throughthe puncture 245, the puncture dilates smoothly, and tearing of vesselwall 240 is reduced or eliminated. The resultant opening 390 in vesselwall 240 is both smaller and smoother than openings 320 or 350 createdby the prior art methods and apparatus as depicted in FIGS. 3B and 3C.If tearing of the puncture does occur, presumably due to the elasticlimitations of vessel wall 240, such tearing is less severe than thatcreated by a conventional prior-art dilator-filament combination.

Other embodiments of the invention include mating configurations of thecircumferential, annular step transition of the filament and the tip ofthe dilator which improve the connection of the two upon abutment of thedilator tip to the step. FIGS. 7A-7C and 8A-8C show these features.

In one embodiment an element is affixed to or is an integral part of theproximally-facing surface of the step which mates with the distal tip ofthe dilator. The proximally-facing surface of such a transition elementthen becomes the proximally-facing surface of the step, or a portionthereof. An advantage of a separate transitional element is that itsproximally-facing surface can be fabricated to be very precise andsmooth so that it will not damage the tip of the dilator. Anotheradvantage is that a specific surface, shape, or contour can be createdwhich, for example, may be complementary to the tip of the dilator.FIGS. 7A-7C show examples of such transitional elements. FIG. 7Aillustrates a transition element 710 for use at the proximally facingsurface of the step of a filament. Transition element 710 is acylindrical, annular element similar to a disc or flat washer. Itprovides a flat, smooth mating surface for the tip of a dilator when thefilament and dilator abut one another.

FIG. 7B illustrates a transition element 720 for use at the proximallyfacing surface of the circumferential step of a filament of theinvention when the step over-shields the dilator tip. Transition element720 is a cylindrical shell with a recessed, proximally-facing annularsurface. Transition element 720 includes outer annular rim surface 722and recessed inner annular surface 724. Transition element 720 thusprovides a recessed, cup-shaped, mating surface for abutting andcapturing the tip of a dilator, and thereby totally protects thedilator's tip when the filament and dilator are assembled. The recess or“cup” of transition element 720 is sized to capture a leading portion ofthe tip of the dilator. FIG. 7C illustrates transition element 720assembled onto filament 400 and capturing the tip of dilator 505.Transition element 710 may be assembled in similar fashion. In allembodiments of the cup-shaped feature, the interior of the recess or cupmay be of various shapes that accommodate the dilator tip.

Embodiments of the invention may further include an element residing inthe step transition region for firmly centering the dilator tip relativeto the circumferential step. FIG. 8A illustrates a hollow,conical-shaped, transition element 830. The outer diameter at the baseof conical transition element 830 is substantially equal to the innerdiameter of the distal tip of the dilator so that the conical structurecan fit inside the tip and center the dilator on the filament.Positioned with its base abutting the end-surface of the proximallyfacing step of the filament, transition element 830 serves as a positivecentering guide for an abutting dilator tip.

The conical centering portion 835 penetrates inside the tip of thedilator to assure optimum concentricity of dilator tip relative to thedistal segment of the filament. A central protrusion on the end-surfacemay be achieved in other ways by various techniques of manufacture. FIG.8B depicts a centering element incorporated into a transition elementsimilar to transition element 710. Transition element 840 comprises aconical portion 845 incorporated into a washer. Transition elements 710,720, 830 and 840 may possess a central bore whose diameter matches or isslightly greater than the outer diameter of the proximal segment of thefilament. Transition elements 710, 720, and 840 have an outer diameterthat is preferably equal to, but in certain cases is less than, theouter diameter of the distal segment of the filament adjacent to thestep. It should be noted that various tapers and rounded contours mayalso achieve such concentricity of the dilator's tip.

FIG. 8C shows transition element 840 affixed to the proximally-facingsurface of the distal segment of the filament 400. Transition elements710, 720 and 730 are affixed to the proximally-facing surface of thedistal segment of the filament in a similar fashion. Transition elements710, 720, 830 and 840 may be adhered, bonded, welded, soldered, orotherwise affixed to the proximal surface of the distal segment of afilament.

Embodiments of the invention may further include coupling mechanisms tosecure the filament to the dilator in an abutting relation to facilitatetheir joint advancement along the tissue track. The dilator may includean integrated coupling incorporated into its hub or incorporated into aseparate structure that is itself coupled to the hub of the dilator.This coupling can be achieved, for example, with an elastomericcompression element that surrounds and engages the filament andcompresses against it. This includes a cylindrical gasket having ahollow bore into which the proximal segment of the filament ispositioned. Mechanical means are provided to compress the elastomericelement around and against the filament such that the frictional forceis sufficient to prevent any relative movement of the filament withinthe compression element. An example of such a coupling is the well-knownTouhy-Borst Adapter.

Alternatively, as shown in FIG. 9A, coupling is accomplished by aknurled screw-down, bolt-like element 910. The threaded bolt 912 iscontained within a housing 914 through which filament 510 passes. Thehousing is positioned in an abutting relationship with the hub ofdilator 505. The bolt's tip (not shown) exerts a compressive forceagainst the filament. The bolt can be tightened until the frictionalforce is great enough to prevent relative movement of the filament andthe dilator. A similar compressive force may be attained by a manual orspring-loaded clamp which is released within a housing to exert acompressive force against the filament.

The inventions may include other types of coupling mechanisms to securethe filament to the dilator when they are assembled. Such mechanismsensure that the dilator and filament are advanced together and do notmove relative to one another, so that firm abutment of dilator tip tostep is maintained for ideal shielding. These coupling mechanisms may beintegrated into one of the components or be a separate element that isattached to the assembly after the dilator tip abuts the filament's steptransition. One alternate embodiment, shown in FIG. 9B, is atight-fitting, frictional, notched fastener 930, which may be similar indesign to a clothespin, or may have a triangulated notch 932. Thisfastener is assembled onto the filament at a position adjacent thedilator's hub and pressed until it reaches a point within the notch thatprovides a tight grasp onto the filament. The fastener is positioned inan abutting relationship with the hub of dilator 505. Alternatively, thefrictional element may be a clip mechanism.

In other exemplary embodiments the proximal segment of the filament or aportion thereof may have its surface abraded, roughened, or otherwisetreated to increase the frictional force between the coupling elementand filament to prevent slipping. This treatment may be limited to asmall area where the guide element exits the back end of the dilatorhub, a preferred location for a coupling mechanism to be placed.

Each dilator shown and discussed above has a tapered region at itsdistal end. As will be understood by the skilled artisan, certain otherfunctional catheter types do not taper, but rather have a uniform outerdiameter at their distal end. Filaments similar to those described canbe used with catheters having a uniform diameter at their distal end andserve to reduce or eliminate the discontinuity between the filament andsuch catheters.

Each dilator shown and discussed above has been described in itssimplest construction with a centric lumen. As will be understood by theskilled artisan, certain other functional catheter types may have alumen that is eccentric, or may have multiple lumens. Filaments similarto those described can also be constructed to have its proximal segmentbe eccentric from the central axis of the distal segment in order tomate with an eccentric lumen in a catheter, yet still serve to reduce oreliminate the discontinuity between the filament and such catheters

It will be appreciated from the foregoing that the invention eliminatesor substantially reduces the step-up in diameter at the advancing tip ofa prior-art dilator, hence eliminating the blunt insertion forcerequired by prior-art apparatus and the resulting trauma to and tearingof the arterial wall at the puncture hole. Embodiments of the presentinvention provide for a smoother and less traumatic passage of thedilator tip through the tissue and vessel puncture hole by providingshielding of the dilator tip.

Although the classical percutaneous SDH technique was originallydeveloped for entry into the femoral artery, more recently thistechnique has been applied to other peripheral arteries which areaccessible beneath the skin. The foremost example of such an alternatearterial site is the radial artery at the wrist. The radial artery hasbecome the second most frequent percutaneous entry site for coronaryangiography and intervention. Although not as large in diameter as thefemoral artery, the radial artery lies closer to the surface of theskin, is more easily palpated and entered by the puncturing needle.Access via the radial artery has the additional benefit of allowing thepatient to ambulate earlier than where access is via the femoral arteryin the thigh. Other sites where the percutaneous technique is performedinclude superficial veins, such as the femoral, brachial, or jugular.The apparatus of the invention are also applicable to accessing theseother peripheral blood vessels

What is claimed is:
 1. An apparatus for percutaneously dilating anorifice in the wall of a blood vessel or other anatomic structurecomprising, in combination: an elongate introducing guide element havinga proximal segment and a distal segment which meet at a juncture, saidproximal segment having a first outer diameter at said juncture and saiddistal segment having a second outer diameter at said juncture greaterthan said first outer diameter, thereby forming an abruptcircumferential step comprising a proximally-facing surface such thatsaid step creates a discrete transition between said proximal segmentand said distal segment, said distal segment comprising a distal tip andan elongate portion extending from said step to said distal tip of saiddistal segment; and a dilator having an interior bore of sufficient sizeto permit said dilator to slide over the entire proximal segment of saidintroducing guide element, said dilator comprising a distal tip having adistally-facing annular surface with an opening into said interior bore,said dilator distal tip having an inner diameter less than said seconddiameter, such that when assembled together said dilator cannot passdistally beyond said step, said dilator distal tip having an outerdiameter equal to said second outer diameter, such that that whenassembled together with said dilator distal tip abutting said step theirrespective outer diameters match one another to provide preciseshielding of said dilator distal tip and a smooth transition from saidintroducing guide element distal segment to said distal tip of thedilator, thereby permitting said dilator distal tip to smoothly entersaid orifice without resistance from said wall of said blood vessel oranatomic structure.
 2. An apparatus as recited in claim 1 wherein atleast a portion of said proximally-facing surface of said step issubstantially perpendicular to a central longitudinal axis of saidproximal segment.
 3. An apparatus as recited in claim 1 wherein at leasta portion of said proximally facing surface of said step is angledproximally or distally at 60 to 90 degrees to the central andlongitudinal axis of the introducing guide element.
 4. An apparatus asrecited in claim 1 wherein said distal segment has a length of 300millimeters or less and said proximal segment has a length of 300millimeters or less.
 5. An apparatus as recited in claim 1 wherein saiddistal segment has a portion of maximum diameter that is at least 3millimeters in length to block the flow of fluid through said openingwhen said introducing guide element resides within said opening.
 6. Anapparatus as recited in claim 1 wherein said proximally-facing surfaceof said step includes a proximally-extending conical portion having abase adjacent said step, said base having a diameter less than the outerdiameter of said distal segment adjacent said step.
 7. An apparatus asrecited in claim 1 wherein said proximally-facing surface of said stepcomprises a proximally-facing contoured surface, and said distal tip ofsaid dilator comprises a distally-facing surface substantiallycomplementary to said proximally-facing contoured surface.
 8. (canceled)9. (canceled)
 10. An apparatus as recited in claim 1 wherein saidproximally-facing surface of said step comprises means to capture thedistal tip of said dilator.
 11. An apparatus as recited in claim 1wherein said proximally-facing surface of said step comprises means foraligning said distal tip of said dilator with respect to the centrallongitudinal axis of said elongate guide element.
 12. An apparatus asrecited in claim 1 further including means for coupling said introducingguide element to said dilator.
 13. An apparatus as recited in claim 12wherein said dilator and said introducing guide element are assembledtogether, with said dilator distal tip abutting said step, and coupledto each other.
 14. An apparatus as recited in claim 1 further includinga coupling mechanism to couple said introducing guide element to saiddilator.
 15. An apparatus as recited in claim 14 wherein said dilatorincludes a hub and said coupling mechanism comprises an elementassembled onto said introducing guide element and adapted to engage withthe hub of said dilator.
 16. An apparatus as recited in claim 14 whereinsaid dilator comprises a compression mechanism adapted to engage saidintroducing guide element.
 17. An apparatus of claim 14 wherein saidproximal segment of said introducing guide element comprises a regionwith a roughened surface to interface with said coupling mechanism. 18.An apparatus of claim 1 further comprising a separate annular transitionelement that is adhered to the proximally facing surface of said step.19. The apparatus of claim 18 wherein said transition element iscylindrical.
 20. (canceled)
 21. An apparatus of claim 1 wherein saiddilator has a maximum outer diameter of 9 French and said introducingguide element comprises an introducing guidewire with a distal segmenthaving a maximum outer diameter of 0.038-inch.
 22. An apparatus of claim1 wherein said introducing guide element includes at least one markingto indicate the distance from said distal tip of said introducing guideelement.
 23. An apparatus of claim 1 further including a couplingmechanism to couple said introducing guide element to said dilator whensaid guide element and said dilator are assembled together in anabutting relationship, said distal segment having a portion of maximumdiameter that is at least 3 millimeters in length to block the flow offluid through said orifice when said guide element resides within saidopening.
 24. (canceled)
 25. (canceled)
 26. (canceled)
 27. (canceled) 28.An apparatus as recited in claim 1 wherein said elongate guide elementcomprises an introducing guidewire having a maximum outer diameter of0.053-inch or less.
 29. (canceled)
 30. (canceled)
 31. (canceled) 32.(canceled)
 33. (canceled)
 34. (canceled)
 35. An apparatus as recited inclaim 1 wherein said proximal segment of said elongate guide element isa core wire, and said distal segment of said elongate guide elementcomprises said core wire and a wire coiled around said core wire, thelast helical coil at the proximal end of said distal segment beingfabricated flat to comprise a portion of said proximally-facing surface.36. (canceled)
 37. An apparatus for percutaneously dilating an orificein the wall of a blood vessel or other anatomic structure comprising: anelongate introducing guide element having a proximal segment and adistal segment which meet at a juncture, said proximal segment having afirst outer diameter at said juncture and said distal segment having asecond outer diameter at said juncture greater than said first outerdiameter, thereby forming an abrupt circumferential step comprising anproximally-facing surface such that said step creates a discretetransition between said proximal segment and said distal segment, saiddistal segment having a portion of maximum outer diameter that is atleast 3 millimeters in length to block the flow of fluid through saidorifice when said portion of maximum outer diameter resides within saidorifice; and a dilator having an interior bore of sufficient size topermit said dilator to slide over the entire proximal segment of saidintroducing guide element, said dilator comprising a distal tip having adistally-facing annular surface with an opening into said interior bore,said dilator distal tip having an inner diameter less than said seconddiameter, such that when assembled together said dilator cannot passdistally beyond said step.
 38. (canceled)
 39. An apparatus as recited inclaim 37 wherein said introducing guide element includes at least onemarking to indicate the distance from the distal tip of said introducingguide element.
 40. (canceled)
 41. An apparatus as recited in claim 37wherein said distal segment comprises a wire coiled around alongitudinal core element and said proximal portion is solely comprisedof said core element.
 42. An apparatus as recited in claim 37 wherein atleast a portion of said proximally-facing surface of said step issubstantially perpendicular to a central longitudinal axis of saidproximal segment.
 43. An apparatus as recited in claim 37 wherein saiddistal segment has a minimum length of 1.0-inches to assure that saiddistal segment has sufficient length to extend through said opening insaid wall of a blood vessel or other anatomic structure and assure thatsaid step resides outside said opening in said wall of a blood vessel orother anatomic structure.
 44. (canceled)
 45. A kit containing componentsof an apparatus for percutaneously creating and accessing an orifice inthe wall of a blood vessel or other anatomical structure comprising, incombination: a tubular device having a sharp distal tip and a hollowbore for percutaneous puncture of said wall to create said orifice; andan elongate introducing guide element for passage through said tubulardevice to access said orifice, said introducing guide element having aproximal segment and a distal segment which meet at a juncture, saidproximal segment having a first outer diameter at said juncture and saiddistal segment having a second outer diameter at said juncture greaterthan said first outer diameter, thereby forming an abruptcircumferential step comprising a proximally-facing surface such thatsaid step creates a discrete transition between said proximal segmentand said distal segment, said distal segment having a portion of maximumouter diameter, said maximum outer diameter matched to the diameter ofthe hollow bore of said tubular device, thereby blocking the flow offluid through said hollow bore when said portion of maximum outerdiameter resides within said hollow bore, said portion of maximum outerdiameter being at least 3 millimeters in length to block the flow offluid through said orifice when said needle is removed and said portionof maximum outer diameter resides within said orifice.
 46. A kit ofclaim 45 wherein said tubular device is a vascular needle.
 47. A kit ofclaim 45 wherein said distal segment has a maximum outer diameter of0.053-inch or less.
 48. A kit containing components of an apparatus forpercutaneously creating and dilating an orifice in the wall of a bloodvessel or other anatomical structure comprising: a needle having ahollow bore for percutaneous puncture of said wall to create saidorifice; and an elongate introducing guide element for passage throughsaid needle to access said orifice, said introducing guide elementhaving a proximal segment and a distal segment which meet at a juncture,said proximal segment having a first outer diameter at said juncture andsaid distal segment having a second outer diameter at said juncturegreater than said first outer diameter, thereby forming an abruptcircumferential step comprising a proximally-facing surface such thatsaid step creates a discrete transition between said proximal segmentand said distal segment, said distal segment comprising one or moreportions having an outer diameter matched to the diameter of said hollowbore of said needle to permit it to block the flow of fluid through thehollow bore of said needle when said distal segment is positionedtherein; and a dilator having an interior bore of sufficient size topermit said dilator to slide over the entire proximal segment of saidintroducing guide element, said dilator comprising a distal tip having adistally-facing annular surface with an opening to said interior bore,said dilator distal tip having an inner diameter less than said seconddiameter, such that when assembled together said dilator cannot passdistally beyond said step, said dilator distal tip having an outerdiameter equal to said second outer diameter, such that that whenassembled together with said dilator distal tip abutting said step theirrespective outer diameters match one another to provide preciseshielding of said dilator distal tip and a smooth transition from saidintroducing guide element distal segment to said distal tip of thedilator, thereby permitting said dilator distal tip to smoothly entersaid orifice without resistance from said wall of said blood vessel oranatomic structure.
 49. A kit containing components of an apparatus forpercutaneously creating and dilating an orifice in the wall of a bloodvessel or other anatomical structure comprising: a needle having ahollow bore for percutaneous puncture of said wall to create saidorifice; an elongate introducing guide element for use with said needlehaving a proximal segment and a distal segment which meet at a juncture,said proximal segment having a first outer diameter at said juncture andsaid distal segment having a second outer diameter at said juncturegreater than said first outer diameter thereby forming an abruptcircumferential step comprising a proximally-facing surface such thatsaid step creates a discrete transition between said proximal segmentand said distal segment, said distal segment having a portion of maximumouter diameter that is at least 3 millimeters in length and of adiameter to permit it to block the flow of fluid through the hollow boreof said needle when positioned therein and to block the flow of fluidfrom said orifice when said needle is removed and said portion ofmaximum outer diameter resides within said orifice; and a dilator havingan interior bore of sufficient size to permit said dilator to slide overthe entire proximal segment of said introducing guide element, saiddilator having a distal tip having a distally-facing annular surfacewith an opening to said bore, said dilator distal tip having an innerdiameter smaller than said second diameter, such that when assembledtogether said dilator cannot pass distally beyond.
 50. A kit as recitedin claim 49 further including an introducing sheath said sheath sized tofit over and around said dilator so as to be carried in tandem with saiddilator during insertion into said orifice.
 51. A kit of claim 49wherein said hollow bore has a maximum diameter of 0.020-inch and saidproximal segment has a maximum diameter of 0.010-inch.
 52. An apparatusas recited in claim 1 further including a sheath sized to fit over andaround the body of said dilator.
 53. An apparatus as recited in claim 1wherein said blood vessel is the femoral artery.
 54. An apparatus asrecited in claim 37 wherein said blood vessel is the femoral artery. 55.An apparatus as recited in claim 37 wherein said proximal segment ofsaid elongate guide element is a core wire, and said distal segment ofsaid elongate guide element comprises said core wire and a wire coiledaround said core wire, the last helical coil at the proximal end of saiddistal segment being fabricated flat to comprise a portion of saidproximally-facing surface.
 56. An apparatus as recited in claim 37wherein said portion of maximum diameter is of a diameter greater thanthe outer diameter at another portion of said distal segment of saidintroducing guide element.
 57. An apparatus as recited in claim 37wherein said proximally-facing surface of said step comprises aproximally-facing contoured surface, and said distal tip of said dilatorcomprises a distally-facing surface substantially complementary to saidproximally-facing contoured surface.
 58. An apparatus as recited inclaim 45 wherein said portion of maximum diameter is of a diametergreater than the outer diameter at another portion of said distalsegment of said introducing guide element.
 59. An apparatus as recitedin claim 45 wherein said distal segment has a portion of maximumdiameter that is at least 3 millimeters in length to block the flow offluid through said opening when said introducing guide element resideswithin said opening.
 60. An apparatus as recited in claim 48 whereinsaid blood vessel is the femoral artery.
 61. An apparatus as recited inclaim 48 further including a sheath sized to fit over and around thebody of said dilator.
 62. An apparatus as recited in claim 48 wherein atleast a portion of said proximally-facing surface of said step issubstantially perpendicular to a central longitudinal axis of saidproximal segment.
 63. An apparatus as recited in claim 48 wherein atleast a portion of said proximally facing surface of said step is angledproximally or distally at 60 to 90 degrees to the central andlongitudinal axis of the introducing guide element.
 64. An apparatus asrecited in claim 48 wherein said proximally-facing surface of said stepcomprises means for aligning said distal tip of said dilator withrespect to the central longitudinal axis of said elongate guide element.65. An apparatus as recited in claim 48 further including a couplingmechanism to couple said introducing guide element to said catheterdilator.
 66. An apparatus as recited in claim 48 wherein saidproximally-facing surface of said step comprises a proximally-facingcontoured surface, and said distal tip of said dilator comprises adistally-facing surface substantially complementary to saidproximally-facing contoured surface.
 67. An apparatus of claim 49wherein said dilating catheter distal tip has an outer diametersubstantially equal to the outer diameter of said distal segmentadjacent said step.
 68. An apparatus of claim 49 wherein said dilatingcatheter distal tip has an outer diameter smaller than the outerdiameter of said distal segment adjacent said step.
 69. An apparatus ofclaim 49 wherein said dilating catheter distal tip has an outer diameterlarger than the outer diameter of said distal segment adjacent saidstep.